Industrial TCAD applications cover a broad range of analysis and synthesis tasks aimed at characterizing fabrication processes, tuning device performance, improving yield numbers, and evaluating and selecting technology alternatives. The role of TCAD and TCAD applications differ from company to company, ranging from the characterization of critical process sequences in a stand-alone fashion using manually written simulator scripts to fully integrated modeling and simulation of actual factory-floor processes and procedures. However, the fact that the number of experimental wafers that can be processed is being steadily reduced by escalating equipment costs and more complex and therefore increasingly time-consuming processes makes TCAD an indispensable methodology for continuing progress in semiconductor development [Mar96].
Figure 2.1 sketches VLSI design loops from circuit specification to process design.
Figure 2.1:
Nested VLSI design loops. Circuit
specifications establish constraints for circuit design, calling
for specific device characteristics to be realized by process design.
The innermost design loop
is based on device fabrication
and represents the most expensive tasks. The target process has to be
tuned to yield devices matching the device specifications derived from
circuit design. Circuit modeling reads device parameters extracted
from device data to simulate the behavior of the target circuit
prototype. Deviations from the circuit specifications - themselves
being imposed by system and product design - lead to an adjustment
of the circuit prototype.
This chapter gives an overview of typical TCAD tasks found in the semiconductor industry and in research laboratories together with a brief summary of applicable TCAD tools and methodologies.